Digital communications systems transmit information originating from an analog or digital signal source. In either event, the information is typically coded into digital words for transmission through a digital facility. The digital words, on average, cannot exceed an allotted number of bits. The allotted number of bits is dependent on a number of factors, such as the digital transmission format and/or the facility channel capacity.
The coding of information into digital words having the allotted number of bits provides a certain precision. In many system applications, however, the precision desired corresponds to the coding of all digital words with more than the allotted number of bits. One example of this situation arises in the digital transmission of video signals.
One prior art approach to reduce the number of bits per digital word for a given precision is to utilize predictive differential coding. In predictive differential coding, the difference between the information to be transmitted and a prediction of this information is coded. When the difference is small, the difference can be accurately represented by a small number of bits. However, large differences cannot be accurately represented by a small number of bits. Therefore, the problem with predictive differential coding is that the precision provided varies with the accuracy of the prediction.